Overhangs Drooping, Sagging or Curling Up

Likely causes, most common first

1. Too little part coolingMost common
   Prusa notes overhangs and bridges sag unless the plastic freezes quickly, and its slicer has a separate bridges fan speed for this. Polymaker: PLA without enough fan curls.
2. Overhangs and bridges printed too fastVery common
   Prusa recommends a lower bridge speed, and OrcaSlicer's slow-down-for-overhangs option slows steeper overhangs further, which it says reduces sagging.
3. Angle too steep, or bridge too longCommon
   Prusa says bridges print well mainly over short distances. Beyond the material's limit the line has nothing to stand on, whatever the settings.
4. Small layers with no time to coolCommon
   Polymaker explains that small sections printed in quick succession land on a layer that is still hot. Minimum layer time settings exist for this.
5. Hot enclosure for PLAOccasional
   Polymaker warns that excess ambient heat makes curling worse and advises against printing PLA fully enclosed.
6. Bridge flow or nozzle temperature too highOccasional
   Prusa suggests lowering bridge flow so the line is pulled tight behind the nozzle; Polymaker notes a slightly cooler nozzle within range can help.
7. Wet filamentLess common
   Polymaker lists moisture as a cause when curling persists after the other fixes.

Fix it, one change at a time

1. Get the fan right. Confirm the part fan spins and its duct is clear. For PLA and PETG use the profile's fan, and set the bridges or overhang fan speed higher than the normal fan, as Prusa suggests. For ABS and ASA, which want little fan, rely on the other steps and on support.
2. Slow overhangs and bridges. Turn on the slicer's overhang detection and slow-down-for-overhangs options, and lower the bridge speed.
3. Set a minimum layer time so small layers have time to cool; Polymaker finds 3 to 5 seconds Starting point suits most materials. Printing two copies at once does the same job.
4. Leave curled-perimeter slowdown on if your slicer has it. OrcaSlicer recommends keeping it enabled unless cooling is very strong or printing is already slow, because curl builds up over several layers.
5. Lower bridge flow a little and test. Prusa's method is to print several copies of a bridging test, each with a different bridge flow, and keep the best.
6. Try a slightly cooler nozzle within the filament maker's range.
7. Open the enclosure for PLA. Remove the lid or open the door.
8. Change the geometry if settings run out. Prusa calls reorienting the part the best solution. Otherwise add support (or a support enforcer in the middle of a long bridge), or change the support threshold so more overhangs get support (raise it in PrusaSlicer and Bambu Studio, lower it in Cura; see Support Settings). See Supports and Overhangs.
9. Dry the filament if curling remains after everything else.

Confirm it is fixed

Print an overhang test with steps of increasing angle, or a short bridging test, before and after each change. Note the steepest angle that prints with a clean underside and edges that stay flat, and the longest clean bridge. Use those limits when deciding where the real part needs support.

Why it happens

Each line of an overhang hangs partly past the edge of the line below. Polymaker describes two forces on that unsupported part: its own weight pulling it down, and stress in the plastic as it cools and shrinks. If the line freezes quickly it holds its shape; if it stays soft, weight wins and it droops. That is why cooling and speed matter most: a slower line spends more time under the fan before the next one lands.

Curling is the other direction: the edge lifts instead of dropping. Polymaker ties it to too little fan on PLA, too much heat around the part, and layers printed so quickly that the one below is still hot. Once an edge has lifted, the next layer is printed onto it, and OrcaSlicer describes curl compounding over several layers, so a small lift grows.

Layer height has a trade-off too. Polymaker points out that thinner layers hang out less per layer but are less rigid, while thicker layers are stiffer but overhang further. Its general finding is that a higher layer height, lower speed and consistent extrusion give the best overhangs.

There is always a limit set by the material and the cooling it tolerates. ABS and ASA cannot take much fan, so they reach that limit at shallower angles than PLA. Past it, support or a different orientation is the fix. See Print Orientation and Support Settings.